Process for preparing a polymeric latex

ABSTRACT

A polymeric latex prepared by aqueous emulsion polymerization of a monomeric mixture comprising styrene and butadiene in the presence of a seed polymer prepared by aqueous emulsion polymerization of styrene and a salt of 2-acrylamido-2-methylpropanesulfonic acid.

This application is a continuation of U.S. patent application Ser. No.09/237,512, entitled Polymeric Latexes With High Multivalent IonStability, filed Jan. 26, 1999, now U.S. Pat. No. 6,184,287 B1, thedisclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to polymeric latexes exhibitingoutstanding tolerance to multivalent electrolytes. More particularly,the present invention relates to polymeric latexes with highmultivalent-ion stability prepared by aqueous emulsion polymerization ofa monomeric mixture in the presence of a seed polymer comprising styreneand the neutralized form of 2-acrylamido-2-methylpropanesulfonic acid.The latexes may be useful in the processing and recovery of naturalresources in the mining, petroleum and geothermal industries as well asin paper and textile coatings and construction mixtures employingsubstantial amounts of inorganic pigments or fillers.

BACKGROUND OF THE INVENTION

Most commercial latexes are classified as anionic. This means that thereis a negative charge on the latex particle. This negative charge can beproduced in several ways: (1) using of anionic monomers such ascarboxylic or sulfonic acids of their salts; (2) the normalincorporation of anionic initiator fragments derived from persulfates;and (3) adsorption of the anionic surfactants used to generate latexparticles and stabilize their growth. Of course, like all salts there isan oppositely charged counterion that is relatively free in the waterphase to keep the overall charge balanced.

The negative charge on the latex particle plays a crucial part in itskeeping the latex stable. Electrostatic repulsion of the like (−)charges keep the particles from clumping together and forming largerclusters that eventually precipitate from the water phase.

Any variable that reduces the effective surface charge decreases thelatex stability. Hence, adding simple salts to a latex can destabilizeit. The cationic portion of a simple salt associates with the negativecharges on the latex and reduces the overall charge at the particlesurface. The effect of the cationic counterion depends upon both itsconcentration and its charge or valency. Thus multivalent cations areespecially harmful in destabilizing anionic latex. The ionic strength isone measure of the destabilizing effect of a solution on latex. Theproduct of the salt concentration and the square of the ionic chargedetermine the ionic strength; therefore, equamolar amounts of Na+, Ca++,and Al+++ have relative effects of 1, 4, and 9 respectively. By usingboth different multivalent salts and different concentrations, one candevise increasingly more severe latex stability tests and establishdifferent echelons of latex stability.

The effect of temperature is also substantial. As the temperatureincreases, eventually the higher kinetic energy of the latex particlesmay allow them to overcome the electrostatic repulsion, collide andcoalesce. Consequently, a combination of high electrolyte concentrationsof multivalent cations and elevated temperatures constitutes anespecially severe set of conditions for latex stability. Indeed,commercial latexes are considered “excellent” if they can withstand theslow addition of 10 mL of 2% calcium chloride to about 50 mL of latex,even at room temperature. It is well known that as the temperature isincreased then the stability of latex in the presence of salts isgreatly reduced. For this reason, room temperature tests are used thatcall for much higher electrolyte concentrations than is actuallyencountered in an application so as to compensate for needing tofunction at higher temperatures. Also, adding a hot salt solution to hotlatex is less convenient as a screening test.

In electrolyte stability testing, the amount of residue or grit that isgenerated when the latex is “shocked” by adding the salt solution ismeasured. Naturally, the identity of the salt and the strength of thesalt solution determine the amount of residue produced. The rate ofaddition of the salt solution, stirring of the latex, etc. can also havean effect in discerning between borderline cases or similar stabilities.The amount of residue generated in the test is not to be confused withgrit or residue that may be formed during the latex manufacturing. Forthis reason the latex is fist filtered free of fine grit prior totesting.

It will be appreciated from the foregoing that latexes having highmultivalent-ion stability may be useful in the processing and recoveryof natural resources in the mining, petroleum and geothermal industriesas well as in paper and textile coatings and construction mixturesemploying substantial amounts of inorganic pigments or fillers.

For example, techniques for drilling and completing wells, particularlygas and oil wells, are well established. Of chief concern here are thosewells which are drilled from the surface of the earth to somesubterranean formation containing a fluid mineral which it is desired torecover. After the fluid containing geologic formation is located byinvestigation, a bore-hole is drilled through the overlying layers ofthe earth's crust to the fluid containing geologic formation in order topermit recovery of the fluid mineral contained therein. A casing is thenpositioned within the borehole to insure permanence of the borehole andto prevent entry into the well of a fluid from a formation other thanthe formation which is being tapped. This well casing is usuallycemented in place by pumping a cement slurry downwardly through the wellborehole, which is usually accomplished by means of conducting tubingwithin the well casing. The cement slurry flows out of the open lowerend of the casing at the well bottom and then upwardly around the casingin the annular space between the outer wall of the casing and the wallof the well borehole.

Gas channeling is a phenomenon that occurs during the setting of thecement slurry. Once the cement slurry begins to set, the hydrostaticpressure in the cement column begins to decrease. This reduction inhydrostatic pressure allows the channeling of gas. This phenomenonoccurs during setting of the cement, from the time when setting hasprogressed enough for the hydrostatic pressure to no longer betransmitted, or to no longer be sufficiently transmitted through thecement, but not enough for the cement at the level of the gas pocket tooppose migration of the gas into the setting cement under the pressurefrom the gas pocket which at this point is no longer balanced by thehydrostatic pressure.

The pressurized gas then migrates through the cement slurry in thecourse of its setting and/or between the cement and the drilledformations, creating a multiplicity of channels in the cement, whichchannels may reach up to the surface of the well. It will be appreciatedthat gas channeling can be exacerbated by the cement's shrinkage andpossibly by liquid losses from the cement slurry through filtration intothe surrounding earth, especially in the area of porous formations, alsotermed “fluid loss”.

Gas channeling is thus a serious drawback leading to weakening of thecement and to safety problems on the surface. Various styrene-butadienelatexes have been used as an additive for oil and gas well cementing,primarily to control gas channeling. For example reference is made toU.S. Pat. Nos. 3,895,953; 3,043,709; 4,151,150 and 4,721,160,incorporated herein by reference. It will be appreciated that cementstypically include calcium, aluminum, silicon, oxygen and/or sulfur andwhich set and harden by reaction with water. These include those cementscommonly called “Portland cements”, such as normal Portland orrapid-hardening or extra-rapid-hardening Portland cement, orsulfate-resisting cement and other modified Portland cements, cementscommonly known as high-alumina cements, high-alumina calcium-aluminatecements. Although the latexes heretofore used have been found tofunction, further improved latexes are desired in systems containingalum, calcium carbonate, gypsum, zinc oxide, aluminum calcium phosphate,natural high-hardness brines, and other multivalent inorganic materials.

It is an object of the present invention to provide a polymeric latexwith high multivalent-ion stability. It is another object of the presentinvention to provide a styrene butadiene based latex functionalized witha sulfonated acrylamide monomer that exhibits high tolerance tomultivalent electrolytes, even at elevated temperatures. Another objectof the present invention is to provide a latex that may be useful in theprocessing and recovery of natural resources in the mining, petroleumand geothermal industries as well as in paper and textile coatings andconstruction mixtures employing substantial amounts of inorganicpigments of fillers. More particularly, it is an object of the presentinvention to provide a polymeric latex with high multivalent ionstability which is relatively inexpensive, and provides superior fluidloss control without adversely affecting other critical properties ofthe cement slurry for oil and gas well cementing. It is yet anotherobject of the present invention to provide a polymeric latex useful asan additive for cement compositions for cementing wells. It has beendiscovered in accordance with the present invention, that a polymericlatex additive comprising styrene, butadiene and2-acrylamido-2-methylpropanesulfonic acid when mixed with cement to forma slurry has the effect of limiting the porosity and blocking gaschanneling. These and other objects and advantages will become moreapparent from the following detailed description and examples.

SUMMARY OF THE INVENTION

Briefly, the present invention relates to a polymeric latex prepared byaqueous emulsion polymerization of a monomeric mixture comprisingstyrene and butadiene in the presence of a seed polymer prepared byaqueous emulsion polymerization of styrene and a salt of2-acrylamido-2-methylpropanesulfonic acid.

Styrene butadiene based latexes functionalized with a sulfonatedacrylamide monomer exhibit surprisingly high tolerance to multivalentelectrolytes, even at elevated temperatures. Such latexes have potentialutility in the processing and recovery of natural resources in themining, petroleum and geothermal industries as well as in paper andtextile coatings and construction mixtures employing substantial amountsof inorganic pigments or fillers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to polymeric latexes comprisingstyrene, butadiene and the neutralized form of the monomer2-acrylamido-2-methylpropanesulfonic acid, also commonly known as AMPS.AMPS is a registered trademark of The Lubrizol Company. The polymericlatexes in accordance with the present invention have been found usefulas an additive to cementing compositions for oils, gas, and geothermalwells. Utility is also anticipated in applications which requirestability of a latex binder in systems containing alum, calciumcarbonate, gypsum, zinc oxide, aluminum calcium phosphate, naturalhigh-hardness brines, and other multivalent inorganic materials.

The polymeric latexes in accordance with the present invention areprepared via a seeded polymerization of a monomeric mixture comprisingstyrene and butadiene using deionized water as a continuous phase, i.e.,aqueous emulsion. The ratio of styrene to butadiene in the polymericlatex is typically about 2:1, although a somewhat higher or lower ratiomay be used. Preferably, the polymeric latexes include about 30 to 80weight percent styrene and about 20 to 70 weight percent butadiene.

The seed used in the aqueous emulsion polymerization is prepared byfirst copolymerizing an aqueous emulsion of a mixture of about 5 to 20weight percent of styrene monomer, preferably about 8 to 12 weightpercent of styrene monomer and from about 5 to 20 weight percent of theneutralized form of the monomer 2-acrylamido-2-methylpropanesulfonicacid, preferably about 5 to 10 weight percent. It will be appreciatedthat levels of the neutralized form of the monomer2-acrylamido-2-methylpropanesulfonic acid above about 10 to 20 weightpercent causes a broad particle size distribution. It has been foundthat the salts of 2-acrylamido-2-methylpropanesulfonic acid providesuperior electrolyte and high temperature resistance to the polymericlatexes in accordance with the present invention in contrast to thecarboxylates, alcohols, phenolics and steric stabilizers typically usedin emulsion polymerization.

The neutralized form of the monomer 2-acrylamido-2-methylpropanesulfonicacid may be formed by the neutralization of the acid monomer with analkaline agent such as a source of sodium, calcium, magnesium, ammoniumions and the like to form the salt of2-acrylamido-2-methylpropanesulfonic acid.

In an alternate embodiment, the seed may be formed by aqueous emulsionpolymerization of a mixture of about 5 to 12 weight percent of styrenemonomer and about 2 to 6 weight percent of butadiene monomer and fromabout 3 to 20 weight percent, preferably about 5 to 10 weight percent ofthe neutralized form of the monomer 2-acrylamido-2-methylpropanesulfonicacid. In yet another alternate embodiment, the seed may be formed byaqueous emulsion polymerization of a mixture of about 5 to 10 weightpercent of styrene monomer and about 2 to 6 weight percent of butadienemonomer and from about 3 to 10 weight percent, preferably about 3 to 5weight percent of the neutralized form of the monomer2-acrylamido-2-methylpropanesulfonic acid and about 2 to 5 weightpercent seed comonomer.

The seed comonomer allows the polymeric latex to reach a stabilityequivalent to formulations containing higher concentration levels of theneutralized form of 2-acrylamido-2-methylpropanesulfonic acid. The seedcomonomers may be selected from acrylonitrile, preferably mildlyhydrophobic acrylamides such as methacrylamide, N-isopropyl- andN-t-butyl acrylamide, and N-(1,1-dimethyl-3-oxobutyl)acrylamide. Alsoeffective as a seed comonomer are di(meth)acrylates with ethylene oxidespacer units in the 5-20 range. Less preferred seed comonomers are C1-C3(meth)acrylates. It will be appreciated that acrylamide has been foundineffective as a seed comonomer and deleterious to polymeric latexproduction.

The above monomers are polymerized in the presence of water, freeradical initiators, anionic surfactants, and chelating agents to formthe latex binder of the present invention using conventional emulsionpolymerization procedures and techniques except as otherwise providedherein.

The free radical initiators utilized to polymerize the monomers of thepresent invention include sodium persulfate, ammonium persulfate,potassium persulfate and the like. Other free radical initiators can beutilized which decompose or become active at the polymerizationtemperature such as various peroxides, e.g., cumene hydroperoxide,dibenzoyl peroxide, diacetyl peroxide, dodecanoyl peroxide, di-t-butylperoxide, dilauroyl peroxide, bis(p-methoxy benzoyl)peroxide, t-butylperoxy pivalate, dicumyl peroxide, isopropyl percarbonate, di-sec-butylperoxidicarbonate, various azo initiators such asazobisdimethylvaleronitrile, 2,2′-azobisisobutyronitrile,2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis-2-methyl-butyronitrile, 2,2′-azobis(methylisobutyrate), andthe like and mixtures thereof. The amount of the free radical initiatoris generally from about 0.1 to 2, and preferably from about 0.5 to 1.0parts by weight per 100 parts by weight of the total amount of monomersadded.

Optional chain transfer agents include mercaptans such as the alkyland/or aryl(alkyl)mercaptans having from about 8 to about 18 carbonatoms and preferably from about 12 to about 14 carbon atoms. Thetertiary alkyl mercaptans having from about 12 to about 14 carbon atomsare highly preferred. Examples of specific chain transfer agents includen-octyl mercaptan, n-dodecyl mercaptan, t-octyl mercaptan, t-dodecylmercaptan, tridecyl mercaptan, tetradecyl mercaptan, hexadecyl mercaptanand the like, as well as mixtures thereof. The amount of the chaintransfer agent utilized is from about 0.2 to 2.5, preferably from about0.5 to 1.5 parts by weight per 100 parts by weight of the total amountof monomers added.

The anionic surfactants include sodium dodecylsulfate, sodiumdodecylbenzene sulfate, sodium dodecylnaphthalene sulfate,dialkylbenzenealkyl, sulfates, sulfonates and the like, especiallypreferred is the dihexyl ester of sodium sulfosuccinate. The amount ofanionic surfactant present is sufficient to obtain an aqueous emulsionof the monomers. Such an amount is typically from about 0.5 to 1.5 partsby weight per 100 parts by weight of the total amount of monomers added.It will be appreciated that the present invention does not require thepresence of additional stabilizers, ionic surfactants, stabilizingsurfactants such as ethoxylates sulfonates and the like in order toattain the high electrolyte tolerances needed.

Chelating agents may also be used during polymerization to tie upvarious metal impurities as well as to achieve a uniform polymerization.Examples of specific chelating agents include ethylene diaminetetra-acetic acid, nitrilotriacetic acid, citric acid, and theirammonium, potassium and sodium salts. The amounts of the chelatingagents may range from about 0.01 to 0.2 parts by weight per 100 parts byweight of the total amount of monomers added.

The polymerization process is effected by the selective addition of thevarious reactants in multiple stages to the reaction zone of a reactoras the reaction continues. The polymerization process is generallycarried out from about 120 to 200 degrees F., and preferably from about150 to 170 degrees F.

The process includes the step of forming a first polymeric seed bycharging into the reaction zone of the reactor an aqueous emulsionpolymerizable mixture of one or more emulsion polymerization monomers asdescribed above, the neutralized form of2-acrylamido-2-methylpropanesulfonic acid, surfactant, chelating agentand initiator. The neutralized form of2-acrylamido-2-methylpropanesulfonic acid must be added in the seed stepalong with the comonomers at a pH greater than 4.5, preferably about 6to 9 to be effective.

In a preferred embodiment, the anionic surfactant, chelating agent andneutralized form of 2-acrylamido-2-methylpropanesulfonic acid and one ormore emulsion polymerizable monomers, are first added to the reactor,heated to about 150 degrees F. and then an aqueous mixture of freeradical initiator is added. The aqueous reactants are allowed to reactand then the temperature is increased to about 170 degrees F.

Subsequently, aqueous emulsion polymerizable mixtures including at leastone polymerizable monomer, about 0.5 to 2.0 wt. chain transfer agent andabout 0 to 5 wt. surfactant are charged to the reaction zone of thereactor over a plurality of stages. In a preferred embodiment, theaqueous polymerizable mixtures are charged to the reactor in a batch ata rate faster than the polymerization rate over about six separatestages such that after each charge the mixture is allowed to reactwithin the reactor. The additional stages include an aqueouspolymerization mixtures of styrene, butadiene and chain transfer agentand optionally surfactant to stabilize growing particles. The emulsionpolymerizable mixture is then allowed to react in the reactor to highconversion, preferably from 97% to nearly quantitative yield.

The invention will be further clarified by a consideration of thefollowing examples, which are intended to be purely exemplary of theinvention. As used in the Examples, Iam=N-Isopropylacrylamide;tBAm=N-t-butylacrylamide; Mam=methacrylamide; Peg-600DMA=Adimethylacrylate crosslinker with '13 ethylene oxide units; TEGDMA=Adimethylacrylate crosslinker with '3 ethylene oxide units;DAAm=diacetoneacrylamide; HMPA=hydroxypropylacrylate; MA=methylacrylate;EA=ethylacrylate; MMA=methylmethacrylate; ACN=acrylonitrile; NaSS=thesodium salt of styrene sulfonic acid; Na=sodium salt; NH4=ammonium salt;NaAMPS=the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid;Bd=1,3-butadiene, and SBA=styrene, butadiene, acrylontrile.

EXAMPLE 1

A one-gallon stainless steel pressure reactor equipped with monomeraddition ports, stirrer and temperature and pressure measurement deviceswas used. Cooling was provided by an external water bath. The amountsprovided below are based on a given concentration of reagent.

A mixture of deionized water 1515 g, ammonium hydroxide (28%) 11.3 g,2-acrylamido-2-methylpropanesulfonic acid 36 g, Citrosol (50%) 3.3 g,hampene Na3 (40%) 1.5 g, Aerosol MA-80 (80%) 20.7 g, styrene 105 g andacrylontrile 60 g was added to the reactor and then heated to 150degrees F. Citrosol is a solution of citric acid and a registeredtrademark of Archer Daniels Midland Company. Aerosol is a registeredtrademark of American Cyanamide Company. Aerosol MA is asurfactant/wetting agent used for reducing the interfacial tensionbetween liquids and solids or between two immiscible liquids. A solutionof ammonium persulfate 6.5 g in deionized water 58.5 g was then added tothe reactor. After 30 minutes the reactor temperature was increased to170 degrees F. and then the following polymerizable mixtures identifiedin stages in Table 1 below were sequentially added every 30 minutes.

TABLE 1 Weight, grams Stage 1 Styrene 112 Sulfole 120 1 Butadiene 52Stage 2 Styrene 112 Sulfole 120 1 Butadiene 52 Stage 3 Styrene 112Sulfole 120 1 2-Hydroxyethylacrylate 8 Butadiene 52 Deionized water 27Stage 4 Styrene 112 Sulfole 120 1 2-Hydroxyethylacrylate 8 Butadiene 52Deionized water 27 Stage 5 Styrene 112 Sulfole 120 1 Butadiene 52 Stage6 Styrene 112 Sulfole 120 1 Butadiene 52

Sulfole is a registered trademark of Phillips Petroleum Company formercaptans.

After the addition of the polymerizable mixture of Stage 6 to thereactor, the polymerizable mixture was then reacted in the reactor untilconstant solids of about 40 to 42%. The conversion of monomers topolymer was about 98%.

Ammonium hydroxide (28%) 23 g, deionized water 66 g, ammonium persulfate1.2 g were added to the reactor and allowed to reactor for 90 minutesand then deionized water 65 g, ammonium persulfate 2.4 g and Drew L1981.8 g were added to the reactor and allowed to react for 30 minutes thencooled and transferred to a stripping vessel and steam stripped andfiltered in a conventional manner. Drew L198 is a blend of mineral oil,silica and alkoxylated fatty derivatives from Ashland Chemical Company.Bostex 490-B AO is an antioxidant supplied by Akron Dispersion Inc. aswell known in the art. Bostex 490-B AO is an aqueous mixture ofditridecyl thiodipropionate, 4-methyl phenol and reaction product ofdicyclopentadiene and isobutylene, sodium dodecylbenzene sulfonate.

The post stripping addition is provided below in Table 2.

TABLE 2 Post Stripping Weight, grams Ammonium hydroxide (28%) 19.2Bostex 490-B AO (35%) 6.2 Proxel (25%) 12.0 Deionized water 36.0

Proxel is a registered trademark of Imperial Chemical Industries Limitedand is a biocide for the preservation of latexes. The polymeric latex inaccordance with the present invention has been found to be particularlyuseful as an additive for a cementing composition.

EXAMPLE 2

Latex samples were prepared in accordance with the present invention,filtered free of residue, and diluted 1:1 with a salt solution (3% NaCl)that was also spiked with 850 ppm calcium ions. This salt water latexsuspension was placed in glass beverage bottle, capped, inserted into ametal bottle guard and rotated slowly in a thermostat water bath at 180degrees F. for 24 hours. After the bottles cooled, the amount of residuewas determined that was generated during the process. A standard latexwill precipitate almost entirely.

The stability of the latexes was then tested. Electrolyte resistance ortest severity is measured by the charge on the positivecounterion-Al+++>Ca++>Na+. That is, testing with an Aluminum salt ismuch more severe than testing with a calcium salt. The amount andconcentration of electrolyte solution added to the latex also measuresstability. For example, adding 20 mL of 5% calcium chloride solution ismore stringent than adding 40 mL of 2.5% calcium chloride solutionbecause of the higher “shocking” (localized concentration) effect of thehigher “strength” solution, even though the total amount of calcium ionsis the same. Just adding more of the same strength solution is lessdiscerning in differentiating between latex samples. Namely, adding 30mL versus 20 mL of 2% calcium chloride is not as severe a test as addinga smaller amount of a more concentrated divalent salt solution.

The generalized test for electrolyte stability is as follows:

A. Filter 75 to 100 g of latex through a 325 mesh screen to provide aresidue-free test sample.

B. Add enough latex to equal 25 g of dry polymer to a small beaker.

C. Add a magnetic stir bar to the beaker with latex and place it on amagnetic stir plate.

D. While the latex is stirring at a medium speed, add the amount ofelectrolyte solution (for example, 20 mL of 20 wt % AlCl₃) at a fastdropwise rate.

E. After all the electrolyte solution has been added, remove the beaker,dilute to 500 mL with distilled water [500−(mL latex+mL salt solution)].

F. Weigh a 100 mesh screen.

G. Filter the 500 mL of diluted latex through the preweighed 100 meshscreen.

H. Dry the screen & any residue formed in the test in an oven toconstant weight. (2 hr @ 275 degrees F. is generally sufficient)

I. Determine the weight of residue on the screen and report as wt % dryresidue on dry polymer solids. That is as a weight % based on the drypolymer.

The results of the test provided below in Table 3.

TABLE 3 Residue² Formed After AMPS¹ 24 Hours @180 Latex/Seed Variation(phm) degrees F. 1 SBA/AMPS + ACN in Seed 3.0 0.00% 2 SB/AMPS in Seed3.0 0.05% 3 SBA/AMPS + ACN in middle 1.5 27.1% of batch 4 SB/ItaconicAcid in Seed None 87.5% ¹AMPS polymerized as the ammonioum salt. phm =the parts per 100 parts monomers based on the free acid of AMPS, 3.25phm based on the ammonium AMPS. ²Residue is the grit captured by a 325mesh standard screen.

Latexes 1 and 3 are styrene, butadiene, AMPS copolymers with a 5 phmacrylonitrile. Latexes 3 and 4 use 0.5 phm itaconic acid in the seedstep, an ingredient that provides improved electrolyte stabilitycompared to other carboxylic acid monomers. Entries with AMPS in theseed do not contain itaconic acid. Latex 4 is a styrene butadienecopolymer with the same butadiene level as the other entries. AMPS andAMPS+ACN variations are made by taking out part of the styrene in therecipe for Latex 4.

Latexes 1 and 2 versus Latex 4 show the significant improvement gainedby copolymerizing with Ammonium AMPS in the seed. Also, Latex 4 showsthe inability of a standard latex to function in hot brine as might beencountered in a geothermal well. Also, Latex 4 would be stable underthese electrolyte concentrations at room temperature. Latex 4 isrepresentative of a composition that does not possess the stability towithstand the lower echelon of electrolyte stability.

EXAMPLE 3

Latexes 1 and 2 from Example 2 were tested to determine the stability incalcium chloride and the effect of the comonomer in the seed. Calciumchloride was added slowly in 60 mL of each latex. The stability test wasrun at room temperature.

TABLE 4 Latex 1 Latex 2 3.0 AMPS + 5.0 ACN in seed 3.0 AMPS in seed MI2% CaCl2 Residue Formed Residue Formed 20.0 0.00 0.00 wt % 30.0 0.001.40 40.0 0.00 75.0

Latex 1 is a copolymer of styrene butadiene using 8.75 phm styrene+5.0phm acrylonitrile as seed monomers along with 3.0 phm of AMPSneutralized to the ammonium salt prior to polymerization.

Latex 2 is a copolymer of stryene butadiene using 13.75 phm styrene asthe seed monomer along with 3.0 phm of AMPS neutralized to the ammoniumsalt prior to polymerization.

Table 4 shows a very slight different in stability between usingacrylonitrile in the seed or leaving it out. This data, testing withlarger amounts of electrolyte, clearly demonstrates the improvedstability gained with the comonomer at this level of AMPS (3.0 phm basedon AMPS or 3.25 phm based on the ammonium salt). Note, the ammonium saltis still used and not the free acid version.

EXAMPLE 4

Latexes were prepared in accordance with the present invention asprovided below in Table 5. Latex 6 comprised 2.5 parts of AMPS added atthe seed stage and then 2.5 parts of AMPS were added later duringpolymerization. In Latexes 7 and 8 all of the AMPS was added in the seedstage of the latex production. Residue levels in the 0.01 to 0.001%level is considered well within the acceptable range for mostapplications and do not necessarily reflect the onset of instability.Namely, such samples may show stability at a higher electrolyte severitywhen tested.

TABLE 5 AMPS Residue Residue Seed After From 2% From 10% Seed Co-monomerAMPS Seed AlCl₃ CaCl₂ Latex 5-None 1.5 0 Failed set-up Failed set-upLatex 6-None 2.5 2.5 90%+ 0.000 Latex 7-None 5.0 none 0.008% 0.000 Latex8-5% 5.0 none 0.000% 0.000 Acrylonitrile

Satin White, a calcium sulfate pigment, is notorious for destabilizingtypical latex binders used in paper coatings. In spite of impartingexcellent optical properties to coated paper, Satin White has seenlimited use because of the lack of an effective, compatible latexbinder. A screening test for latex compatibility with Satin White is theability to withstand shocking by a 5 wt. % aqueous calcium chloridesolution. Indeed, even higher stability, such as 10 wt. % calciumcarbonate, may be required. Thus, latex binders comparable to Latex 6, 7and especially 8 but also with a 1,3-butadiene content suitable forpaper coating binders (about 30 to 60 wt. %) have utility inapplications requiring high tolerance to multivalent electrolytes, suchas in Satin White based paper coatings.

EXAMPLE 5

Eighteen different latex samples were prepared as provided below inTable 6. All latex samples contained 25.9 parts 1,3 butadiene and 1.3parts of 2-hydroxyethylacrylate which were added in six increments afterthe seed reaction 3 to 5 phm of AMPS based on free acid monomer butpolymerized as the ammonium salt; except for entries 24 and 25 whichwere polymerized as the sodium salt.

The effect of AMPS level and seed comonomer composition on AlCl₃stability was then determined. 10 mL of 2% AlCl₃ was added slowly to 50mL of each latex. The results are provided below in Table 6.

TABLE 6 Co-monomer Residue from Latex AMPS (phm) Co-monomer (phm) 2%AlCl₃ 9 3.0 Iam 5.0 0.000 10 3.0 TBAm 5.0 0.000 11 3.0 Mam 5.0 0.000 123.0 Peg- 5.0 0.000 13 3.0 600DMA 5.0 8.80 14 3.0 DAAm 3.0 0.175 15 3.0DAAm 2.5 1.14 16 3.0 HMPA 2.0 8.87 17 3.0 TEGDMA 5.0 13.67 18 3.0 MA 5.0set-up 19 3.0 EA 5.0 set-up 20 3.0 MMA 2.5 11.81 21 4.0 MMA 5.0 1.26 224.5 ACN 5.0 0.000 23 5.0 ACN 5.0 0.000 24 5.0 ACN 0 0.008 25 5.0 None 00.000 26 3.0 None 0 failed

EXAMPLE 6

A one-gallon stainless steel pressure reactor equipped with monomeraddition ports, stirrer and temperature and pressure measurement deviceswas used. Cooling was provided by an external water bath.

A mixture of deionized water 1600 g, Aerosol MA-80 (80%) 25.9 g SodiumHydroxide (13%) 16.2 g, Sodium AMPS (50%) 300 g, Hampene Na3 (40%) 1.9g, and styrene 131.2 g was added to the reactor. The reactor wasevacuated under low pressure and filled with nitrogen twice. The reactorwas heated to 150 degrees F. A solution of sodium persulfate 8.2 g indeionized water 75 g was then added to initiate polymerization of theseed stage. The seed stage used 8.75 phm (parts per 100 parts monomer)and 10 phm Sodium 2-Acrylamido-2-methylpropanesulfonate (NaAMPS). After45 minutes the reactor temperature was increased to 170 degrees F. andthe remaining monomers (81.25 phm) were added in 10 stages at 40 minuteintervals so as to facilitate temperature control and heat removal. Thefirst three (1-3) and last three stages (8-10) each consisted of thefollowing: 1,3-butadiene 39 g, Sulfole-120 0.8 g, and styrene 80.8 g.While stages 4-7 each contained: styrene 80.9 g. 1,3-butadiene 39 g.Sulfole-120 0.8 g, deionized water 17 g, and 2-hydroxyethylacrylate 5 g.A solution of sodium persulfate 2.7 g in deionized water 75 g was addedto the reactor 40 minutes after the stage 10. Two hours later a mixtureof sodium hydroxide (13%) 5.8 g. sodium persulfate 1.5 g, Drew L-198defoamer 3.8 g, and deionized water 75 g was added. After 30 minutes ofadditional mixing, the latex was cooled and removed from the reactor.After stripping of residual monomers the latex was posted with thefollowing: Proxel (25%) 15.0 g, Wingstay L (50%) 6 g, sodium hydroxide(13%) 6.5 g, and deionized water 30 g.

A series of latex samples were made according to Example 6. Eachcontained 8.75 phm styrene in the seed stage along with NaAMPS and anyother seed monomer specified in Table 7. All contained 26 phm1,3-butadiene added in stages 1-10 and 1.3 phm 2-hydroxyethylacrylateadded in stages 4-7. The styrene added in stages 1-10 was adjustedaccording to variable seed amounts to keep the total monomers at 100parts.

TABLE 7 Electrolyte Tolerance Seed Monomers Latex Stability Residue fromLa- NaAMP Other Other Coagulum Filter 20 mL/ tex S (phm) (phm) variableswt % ability 20% AlCl3 27 5.00 None — 0.02% Good 0.00% 28 3.50 1.5 —0.23% Fair 3.60% NaSS 29 3.50 None 1.5 NaSS 2.65% Poor 0.00% addedstages 4-7 30 None 5.0 — (100%) Latex Not NaSS failed Measurable 31 5.50None — 0.03% Excel- 0.00% lent 32 5.5 5.0 — 0.04% good 0.00% tBAm 33 7.55.0 Bd — 0.04% good 0.00% 34 None 7.5 — (100%) Latex Not NaSS failedMeasurable 35 10.0 None — 0.10% Excel- 0.00% lent 36 10.0 5.0 — 0.09%Good 0.00% Mam 37 12.5 None — 0.03% Excel- 0.00% lent 38 15.0 None —0.15% Good 0.015% 39 17.5 None — 0.10% Good 0.004% 40 20.0 None — 0.32%Fair 0.004%

It was surprising to find that up to 20 phm of a water soluble monomersuch as NaAMPS can be added to the seed stage and still make anacceptable latex. See latexes 35, 37, 38, 39, 40 and 41.

Latexes 30 and 31 show that under the same conditions that work forNaAMPS another common sulfonate monomer NaSS, sodium styrene sulfonate,does not allow a latex to be made. Moreover, comparing latex 27 to latex28 indicates that adding NaSS in the seed detracts from the electrolytetolerance versus an equal weight of NaAMPS. Latex 29 shows that NaSSdoes not detract from the electrolyte tolerance if added later in stages4-7. Latexes 28, 29, 30, and 31 all show the advantages of using NaAMPSexclusively as the sulfonate monomer.

Latexes 32, 33, and 36 show that additional comonomers can still beadded to the seed in combination with higher NaAMPS levels. However,unlike the latex samples using 2.5 to 4.5 phm NaAMPS in the seed, wehave not detected additional stability associated with these comonomers.This is because the NaAMPS samples in the range of from 5 to 12.5% areso stable. Likewise, we cannot at this time show an advantage forincreasing the NaAMPS level in the seed beyond about 12.5 phm. In bothcases extremely severe electrolyte tolerances may be required inspecialized applications where the advantages of higher NaAMPS and/or incombination with comonomers will be seen. There is a distinct trend thatincreasing beyond about 12.5% NaAMPS reduces the latex filterability (anindication of fine residue).

Latex 33 was added simply as an example of using a comonomer. A 7.5 phmNaAMPS seed makes an excellent latex. Latex 33 still uses 26 phm Bd instages 1-10 (that is, 31 phm total).

EXAMPLE 7

TABLE 8 Electrolyte Tolerance Seed Monomers Residue from 40 mL LatexAMPS (salt) Comonomer of 20% AlCl3 41 5.5 (Na) None 0.000% 42 10.0 (NH4)None 0.000% 43 5.4 (NH4) 5.0 IAm 0.000% 44 5.5 (Na) 5.0 IAm 0.000% 4515.0 (Na) None 0.015%

The seed monomers are monomers which in addition to 8.75 phm styrene areadded to the seed stage. The remainder of the monomers were added in sixstages as in Example 1 (same amounts of 1,3-butadiene and2-hydroxyethylacrylate). Latex 42 differs in that 13.75 phm of styrenewas added with 10 phm of ammonium AMPS in the seed; all others used 8.75phm.

Table 8 shows that a number of latexes will withstand twice as muchAlCl₃ as used in Table 7. This is an echelon of electrolyte tolerancethat should be sufficient for all applications at ambient temperaturesand most applications at the high temperatures where the effect ofelectrolytes becomes more stringent. Latex 42 shows that up to about 24phm monomer can be used in the seed. Other entries show that varioussalts of AMPS are essentially equivalent.

EXAMPLE 8

Latexes were prepared in accordance with the present invention wherein aseed stage using styrene and other monomers as shown below was followedby ten monomer additions.

TABLE 9 Sulfonate Residue Monomer from 20 in Seed Seed Added mL 20%Sample Bd (phm) Step (other) Later AlCl3 46 60.0 5.0 none None 0.2%NaAMPS Latex 60.0 5.0 NaSS None Latex failed in coagulated process 4860.0 None 1.5 5.0 NaSS 14.8% Itaconic in middle acid of process

In Table 9, Latex 46 demonstrates that a high-butadiene latex can bemade with outstanding electrolyte stability. That is, the process is notlimited to low butadiene or high Tg materials. The latex that failedfollowed a standard AMPS recipe (Example 5) but tried to use anothersulfonate monomer, sodium styrene sulfonate, in the seed step. This isimportant since it shows the specificity of the invention to AMPS salts.

Latex 48 shows that a measure of stability can be achieved with sodiumstyrene sulfonate but only if this monomer is restricted from the seed.Also, NaSS is far less effective on a weight basis and is currently morecostly. Other data shows that NaSS can be used in combination with AMPSbut that the efficiency is reduced versus using all AMPS,

The latexes in accordance with the present invention have improvedmultivalention tolerance which is important for applications where thelatex is used with fillers such as calcium carbonate. Carpet backing andpaper coatings are two such applications. Furthermore, as shown above,the polymeric latexes in accordance with the present invention have beenfound to have improved multivalent electrolyte and high temperaturestabilities over typical styrene-butadiene latexes.

The cement forming part of the cementing composition can be taken fromany class of common hydraulic cements routines used to cement oil andgas wells. The term “hydraulic cement” is used to designate cementswhich contain compounds of calcium, aluminum, silicon, oxygen and/orsulfur and which set and harden by reaction with water. These includethose cements commonly called “Portland cements”, such as normalPortland or rapid-hardening or extra-rapid-hardening Portland cement, orsulfate-resisting cement and other modified Portland cements, cementscommonly known as high-alumina cements, high-alumina calcium-aluminatecements; and the same cements further containing small quantities ofaccelerators or retarders or air-entraining agents, as well as Portlandcements containing secondary constituents such as fly ash, pozzolan andthe like.

The amount of polymeric latex added to the cement may be varied asdesired. The polymers are generally added in an amount of from about 5to 30 percent based on the weight of the cement. In a preferredembodiment, the polymeric latex comprises from about 10 to 20, mostpreferably, about 15 percent by weight of the cement. Generally, as thetemperature and hardness of the wellbore fluids increase then more latexthat must be used. However, for the current invention, owing to itsstability, 15 to 20 percent latex is still effective under mosttemperatures and hardness levels encountered. The amount of water addedon weight of cement (WOC) is about 35 to 50 percent, corrected for theamount of water in the latex. The latex may be diluted with theappropriate amount of water and added directly in the cement. It will beappreciated that since the polymeric latex is dispersed in the aqueousmedium it is possible to use a high percentage of the polymer withoutimparting high viscosity to the cement slurry.

One or more defoamers may also be added to the cement composition. Thedefoamers are added for their deairentrainment properties imparted tothe resulting cement composition. Any one of a number of defoamersavailable to those skilled in the art may be utilized. A suitabledefoamer is available from BASF Corporation under the trademarkPLURACOL® 4010. This is a polypropylene glycol with an average molecularweight of about 3300. The defoamer is typically added to the compositionin an amount of from about 0.01 to 0.1% based on the weight of thecement.

In some instances certain other additives known as retarders oraccelerators may be added to the cement composition to adjust thethickening time of the cement slurry for the drilling operation. Theseadditives are often added in quantities of from about 0.5 to 1.5%. U.S.Pat. No. 4,537,918, incorporated herein by reference, describes many ofthe known accelerators and retarders available to those in the art. Inaddition to these additives certain other additives may also be used.For example, silica flour may be added in amounts of from about 30 to35% by weight of the cement if the temperature of the oil well isgreater than 220 degrees F. Since Portland cement experiences strengthretrogression at high temperatures, silica flour can be added toincrease the compressive strength of the cement composition.

The physical properties of the cement slurry compositions according tothe various embodiments of the invention should be as follows: the fluidloss should be less than about 55 mL/30 minutes, preferably less thanabout 50 mL/30 minutes, and more preferably less than about 40 mL/30minutes. The plastic viscosity of the composition should be less thanabout 100 cp, and more preferably less than about 50 cp. Additionally,the yield point should be less than about 20 lbs./100 ft². The freewater value should be less than or equal to about 3.

It has been observed experimentally that the presence of the polymericlatex in accordance with the present invention improves the control ofgas channeling in the cemented annulus.

The patents and documents described herein are hereby incorporated byreference.

Having described presently preferred embodiments of the invention, theinvention may be otherwise embodied within the scope of the appendedclaims.

What is claimed is:
 1. A semi-batch aqueous emulsion polymerizationprocess for preparing a polymeric latex having high multivalent ionstability comprising the steps of: preparing a polymer seed by aqueousemulsion polymerization of styrene and a salt of2-acrylamido-2-methylpropanesulfonic acid; and polymerizing a monomericmixture of styrene, butadiene, and optionally a nonionic monomer in thepresence of the polymer seed, whereby the monomeric mixture is added instages.
 2. The process of claim 1, wherein the monomeric mixture isadded in about 3-16 stages.
 3. The process of claim 1, wherein the pHduring the preparation of the seed polymer is about 4.5.
 4. The processof claim 1 wherein the pH during the preparation of the seed polymer isbetween 6-9.
 5. The process of claim 1 wherein the seed polymer isprepared with 0.8 to 1.6 phm of the salt of the dihexylester ofsulfosuccinic acid as the primary emulsifier.
 6. The process of claim 5wherein the seed polymer is prepared with 0.8 to 1.6 phm of the salt ofthe dihexylester of sulfosuccinic acid as the sole emulsifier.